1. Field of the Invention
This invention relates to a motor control system, which generates a motor driving signal according to a speed reference signal that is input at regular updating cycles from a master control system, which is an external apparatus.
2. Description of the Related Art
As shown in FIG. 6, a conventional type of motor control system controls the feedback of speed and current. In the motor control system shown in FIG. 6, a speed reference signal .omega.r* input from a master control system 1 is converted into current references Id*, Iq* by an automatic speed regulator (ASPR) 2. Then the current references Id*, Iq* are converted into voltage references Vd*, Vq* by an automatic current regulator (ACR) 3 and the voltage references Vd*, Vq* output from the automatic current regulator 3 are supplied to a pulse width modulator 4. In the pulse width modulator 4, ON pulse commands Gu, Gv, Gw are generated based on the voltage references Vd*, Vq* and supplied to a power converter 5. In the power converter 5, DC voltage Vdc supplied from a DC power source is converted into desired AC voltage VM by the ON pulse commands Gu, Gv, Gw. A motor (IM) 6 is driven by the desired AC voltage VM supplied from the power converter 5. The speed reference signal .omega..sub.r * from the master control system 1 is updated at a regular cycle and the speed reference signal .omega..sub.r * from the master control system 1 is input at every computing cycle of the control system.
In the above construction, the automatic speed regulator 2 has proportion(P) and integration (I) computing function. In the automatic speed regulator 2 when a deviation(W.sub.rd) is produced between the speed reference signal .omega.r* and a speed .omega. detected by a speed detector (S.S.) 7, the current references I.sub.d *, Iq* are output to reduce the deviation. Further, the automatic current regulator (ACR)3 also has the proportion(P) and integration(I) computing function. In the automatic current regulator 3 when a deviation is produced between the current references I.sub.d *, I.sub.q * and the motor currents Id, Iq detected by a current detector 8, the voltage references V.sub.d *, V.sub.q * are supplied to the power converter 5 via the PWM converter 4 so as to reduce the deviation.
In case of the conventional control system described above, if a response of the motor control system is quick, the speed reference signal becomes the shape of stairs as shown in FIG. 7(a) when the updating cycle T.sub.M of the speed reference signal .omega..sub.r * input from a master control system 1 is longer than the computing cycle T.sub.D of the motor control system. Therefore, the speed reference signal .omega..sub.r * current references I.sub.d *, I.sub.q *, voltage references V.sub.d *, V.sub.q * and furthermore, the motor current I that is supplied to the motor 6 are controlled intermittently as shown in FIG. 7(b) so that they are supplied only when a deviation is produced in the speed reference signal and the torque pulsation will appear as a result. However, it is economically disadvantageous to make the updating cycle of the master control system 1 short in order to suppress it and if the response of the motor control system is made slow, it is not advantageous as the deterioration of efficiency results.